Which of the following is associated with single balanced modulator circuit :
double side band transmission
What a balanced modulator does. It is a multiplier arranged so that the carrier cancels at the output while the sidebands survive. Physically it is two modulator elements (diodes, FETs or a transistor pair) driven in anti-phase by the carrier and in phase by the message, so the carrier terms subtract and the product terms add.
Step 1 — the mathematics of the cancellation. Ordinary AM is
\(s(t)=A_c\left[1+m(t)\right]\cos\omega_c t = A_c\cos\omega_c t + A_c m(t)\cos\omega_c t\)
The first term is the carrier and carries no information; the second holds both sidebands. A balanced modulator removes the first term, leaving
\(s(t)=A_c\,m(t)\cos\omega_c t\)
which is DSB-SC — double sideband, suppressed carrier.
Step 2 — count the sidebands. For a single tone \(m(t)=\cos\omega_m t\), the product-to-sum identity gives
\(A_c\cos\omega_m t\cos\omega_c t=\dfrac{A_c}{2}\cos(\omega_c-\omega_m)t+\dfrac{A_c}{2}\cos(\omega_c+\omega_m)t\)
Two lines survive, one either side of the (absent) carrier — hence double sideband. A single balanced modulator does nothing to remove one of them.
Step 3 — why the other options need extra hardware.
SSB (option 1) needs the DSB-SC output to be passed through a sharp sideband filter, or needs the phase-shift (Hartley) method with two balanced modulators and 90° networks. The balanced modulator alone cannot do it.
VSB (option 3) likewise requires a specially shaped vestigial filter after the modulator, used in analogue television video transmission.
DSB with full carrier (option 4) is exactly what a balanced modulator is designed not to produce — the whole point of balancing is to suppress the carrier, which is where two thirds of the transmitted power would otherwise be wasted.
Single versus double balanced. A single balanced modulator suppresses only the carrier; a double (ring) balanced modulator suppresses both the carrier and the modulating signal, leaving only the sidebands, and is the standard building block of the ring demodulator and mixer.
Hence, a single balanced modulator is associated with double side band transmission.
Similar Questions
Assertion (A) : In amplitude modulation technique the modulation index should be close to 1.
Reason (R) : The power carried by message signal in the side bands increases with increase in modulation index.
Read the statements :
i. DSB has two side bands and SSB has one
ii. DSB has carrier and two side bands and SSB has a carrier and a side band
iii. DSB has carrier and two side bands and SSB without carrier and two different side bands.Which statements are correct ?
Assertion (A) : Amplitude modulation is wastage of power.
Reason (R) : Amplitude modulation is wastage of bandwidth.
The peak carrier voltage is 150 V. If the resistor is 200 Ω and the modulation index is 0.5, the total power in the AM signal is :
In amplitude modulation:
A. Amplitude of carrier is varied by modulating signal
B. Modulation index is between 0 and 1
C. Bandwidth is infinite
D. Bandwidth is twice of minimum modulating frequency.
Choose the correct answer from the options given below:
Match List I with List II
LIST I LIST II A. Power of AM Wave I. \(P_c\left(\frac{m^{2}}{4}\right)\) B. Power of VSB II. \(\frac{m^{2}}{4}P_c+F\left(\frac{m^{2}}{4}P_c\right)\) C. Power of SSB III. \(\frac{m^{2}}{4}\left(\frac{V_c^{2}}{2R}\right)+\frac{m^{2}}{4}\left(\frac{V_c^{2}}{2R}\right)\) D. Power of DSBSC IV. \(\frac{V_{carr}^{2}}{R}+\frac{V_{LSB}^{2}}{R}+\frac{V_{USB}^{2}}{R}\) Choose the correct answer from the options given below:
If 1 MHz carrier is amplitude modulated with a 5 kHz audio signal, the Upper Side Band (USB) and Lower Side Band (LSB) frequencies are ________ respectively.
The modulation index of an AM wave is given by :
Consider an AM (amplitude modulated) signal
\(s(t) = 20\left[1 + 0.9\cos 2\pi \times 10^4 t\right]\cos 2\pi \times 10^6 t\)
The power efficiency (η) in the AM signal is
Important Questions from Amplitude Modulation
- An amplitude modulated voltage signal $x(t)$ drives a load of $1\ \Omega$. $$x(t) = K \cos(300\pi t) + L \cos(240\pi t) + L \cos(360\pi t).$$ If the efficiency is $60\%$, and the carrier power is $50\text{ W}$, the value of $L$ is ______ V.
A 2KW carrier is to be modulated to a 90% level. The total transmitted power would be__________.
Assertion (A) : In amplitude modulation technique the modulation index should be close to 1.
Reason (R) : The power carried by message signal in the side bands increases with increase in modulation index.
Read the statements :
i. DSB has two side bands and SSB has one
ii. DSB has carrier and two side bands and SSB has a carrier and a side band
iii. DSB has carrier and two side bands and SSB without carrier and two different side bands.Which statements are correct ?
Assertion (A) : Amplitude modulation is wastage of power.
Reason (R) : Amplitude modulation is wastage of bandwidth.
